1. Field of the invention
The present invention relates generally to apparatus to be used for treating surfaces of semiconductor wafers, glass plates for photomasks or the like (hereinafter referred to simply as "wafers"). More particularly, it relates to an apparatus capable of supplying a treatment liquid to an upper surface of a wafer at a stroke and uniformly without causing any uneveness through a nozzle for discharging the treatment liquid.
2. Description of the Related Art
Surface treating apparatus of this type are disclosed in, for example, Japanese Patent Laying-Open Nos. 59-126633 land 61-160930, Japanese Utility Model Laying-Open No. 63-50125, . FIG. 1 shows the apparatus disclosed in Japanese Utility Model Laying-Open No. 63-50125.
Referring to FIG. 1, this apparatus comprises: a spin chuck 101 for holding a wafer W horizontally in a rotatable manner; a nozzle 105 for supplying a treatment liquid Q to the upper surface of the wafer W which is maintained horizontal; means, not shown, for moving the nozzle 105 over the wafer W in a direction shown by an arrow F while the nozzle 105 is supplying the treatment liquid Q; and a cup 110 surrounding the wafer W, for preventing scattering of splashes of the treatment liquid. This apparatus is disposed between a wafer conveying unit 111 for conveying the wafer to an apparatus for a posterior processing and a wafer transferring unit 112 for transferring the wafer W to the spin chuck 101.
The wafer carrying unit 111 includes elongated 0-rings 113 on which the wafer is to be moved toward the apparatus for the posterior processing, and pulleys 114 for rotating the 0-rings 113 in a predetermined direction.
The apparatus further has a lifting unit, not shown, for moving the spin chuck 101 vertically.
Referring to FIGS. 1 and 2, this known apparatus operates as follows. First, the spin chuck 101 is raised by the lifting unit so that the top portion of the chuck is at the same level as a plane at which the wafer W is transported. The wafer transferring unit 112 then moves a wafer W on the spin chuck 101. The spin chuck 101 holds the wafer W by a mechanical device or a vacuum contact mechanism. The spin chuck 101 is lowered to a prescribed position while holding the wafer W. When the spin chuck 101 lowers the wafer W to a prescribed level, it rotates the wafer W horizontally. i.e. about a vertical axis over the wafer W in the direction of the arrow F while dispersing the treatment liquid Q through an outlet hole 108 onto the upper surface of the wafer W. See FIG. 2.
The treatment liquid Q is dispersed downward in a fanwise manner to cover the whole surface of the wafer W. Since the wafer W is rotating, excess treatment liquid scatters around the rotating wafer. The scattering treatment liquid strikes against the inner surface of the cup 110 flows downward along the inner surface of the cup 110 and is collected at the bottom.
After a layer of the treatment liquid is formed on the wafer W, the nozzle 105 is moved to a position that does not obstruct vertical movement of the wafer W. The spin chuck 101 raises again the wafer W to the level defined by the wafer conveying unit 111 and the wafer carrying unit 112. The wafer transferring unit 112 receives the wafer W from the spin chuck 1001 and places the wafer on the unit 111, and the wafer is transferred for subsequent processing.
In the above-described conventional apparatus, the treatment liquid Q is dispersed downward in a fanwise manner. Consequently, a sufficient amount of the treatment liquid is supplied uniformly over the whole surface of the wafer. However, this apparatus has certain disadvantages, as described below.
In order to enable the fanwise scattering treatment liquid to cover the entire upper surface of the wafer W, it is necessary to locate the nozzle 105 at a position that is sufficiently high relative to the wafer W. The location of the nozzle 105 is therefore to be higher than the wafer W by 5cm or more. In addition, it is necessary to apply a certain pressure to the treatment liquid to be supplied to the nozzle 105. For instance, it is necessary to apply pressure of about 0.6 kg/cm.sup.2 to the treatment liquid. Because of the application of the pressure to the treatment liquid and the level difference between the nozzle and the surface of the wafer W, the treatment liquid scattering like a shower strikes on the surface of the wafer W, causing an inherent uneveness on the wafer W. This uneveness lowers the yield of production of wafers for which a high quality is required.